The present invention relates, in general, to electronics, and more particularly, to methods of forming semiconductor devices and structure.
In the past, the semiconductor industry utilized various methods to provide high density semiconductor devices and particularly high density transistor structures. The source region of some transistors was produced as a long narrow stripe. One such stripe transistor structure is disclosed in U.S. Pat. No. 6,204,533 issued to Williams et al on Mar. 20, 2001, which is hereby incorporated herein by reference. FIG. 1 illustrates in a general way some of the elements of one example of a prior art stripe transistor 100. Transistors implemented as a stripe structure typically had a body contact diffusion region or body contact formed within a source region. The body contact extended through the source region to make electrical contact to a body region 106. The source region had a physical length 102 that extended along the stripe and a physical width 104. The body contact occupied an area of the source region and had a width 105. The body contact was positioned a distance 103 from the edge of the gate insulator to silicon interface of the transistor in order to prevent the body contact from creating an inactive area along the source region stripe. Distance 103 allowed current to flow through the portion of the source region that was between the gate and the body contact when transistor 100 was enabled. Distance 103 typically was large enough to ensure that some of the source region was always between the body contact and the gate even if there was misalignment during the manufacturing process. Thus, the minimum value of distance 103 typically was at least about one-half of the value of the minimum resolvable dimension of the photolithography techniques used to manufacture transistor 100. As a result, the minimum value of width 104 was about two times the minimum resolvable dimension. This large width reduced the density of the transistor, increased source resistance, and increased the manufacturing cost. Another important parameter of the transistor was the body region resistance or body resistance. Distance 103 increased the body resistance and the corresponding value of the voltage in the body region or body voltage of transistor 100. The increased body resistance and corresponding body voltage reduced the latch-up immunity of transistor 100.
FIG. 2 illustrates in a general way some of the features of an embodiment of another prior art stripe transistor 170. Transistor 170 was a lateral transistor that had a source region 171 positioned within a body region of transistor 170. Source region 171 had a physical width 178. A gate 174 was interposed between source region 171 and drain regions 172. Body contacts 173 were positioned within each source region 171 to electrically contact the body region. Each body contact 173 was spaced a distance 177 from each gate 174. Distance 177 was similar to distance 103 in FIG. 1. A metal contact area 176, illustrated by a dashed line, extended along the surface of region 171 in order to make electrical contact to source region 171 and body contacts 173. Body contacts 173 were positioned within region 171 as a diamond shape relative to the orientation of the sides of source region 171. The diamond shape provided a high probability of forming good electrical contact to source region 171 and body contact 173 even when contact area 176 was misaligned to body contacts 173. However, the dimension of contact 173 parallel to the edge of the gate was reduced and the source edge along the contact area increased correspondingly, thereby decreasing effective source resistance. The increased body resistance and corresponding body voltage reduced the latch-up immunity of transistor 170. However, distance 177 typically was the same as distance 103 that was illustrated in FIG. 1, and the minimum value of width 178 typically remained at least about two times the minimum resolvable dimension. Although source resistance decreased, this large width reduced the density of transistor 170, increased the manufacturing cost, and maintained increased body resistance and susceptibility to latch-up.
Some other transistors were formed as a number of square cells with the source region within the square and the body contact within the source region. One example of such a transistor structure is disclosed in U.S. Pat. No. 5,034,785 issued to Richard Blanchard on Jul. 23, 1991, which is hereby incorporated herein by reference. FIG. 3 illustrates in a general way some of the elements of an example of a square cell transistor 150. Each body contact had a width 151 that typically had a value of the minimum resolvable dimension of the photolithography process. Each side of the body contact was spaced away from the gate by a distance 152 in order to prevent forming an inactive area in the source region and to ensure that the source region and the channel region could support the desired current flow of transistor 150. Typically, the minimum value of distance 152 was about one-half of distance 151. The total width 153 of the source region was a distance equal to width 151 plus two times distance 152, which typically was a distance of about two times the minimum resolvable dimension, thus, the minimum source area was about four times the minimum resolvable dimension. This large cell size resulted in a low density which increased manufacturing costs. Distance 152 also increased the body resistance and corresponding body voltage of transistor 150. The increased body resistance and corresponding body voltage reduced the latch-up immunity of transistor 150.
Accordingly, it is desirable to have a transistor structure that has a small area, a low body resistance, a high latch-up immunity, and a high packing density.
For simplicity and clarity of illustration, elements in the figures are not necessarily to scale, and the same reference numbers in different figures denote the same elements. Additionally, descriptions and details of well-known steps and elements are omitted for simplicity of the description.